Adipocyte Homeostasis Research Articles

Dysfunctional adipocytes promote tumor progression through YAP/TAZ-dependent cancer-associated adipocyte transformation

Obesity has emerged as a prominent risk factor for the development of malignant tumors. However, the existing literature on the role of adipocytes in the tumor microenvironment (TME) to elucidate the correlation between obesity and cancer remains insufficient. Here, we aim to investigate the formation of cancer-associated adipocytes (CAAs) and their contribution to tumor growth using mouse models harboring dysfunctional adipocytes. Specifically, we employ adipocyte-specific BECN1 KO (BaKO) mice, which exhibit lipodystrophy due to dysfunctional adipocytes. Our results reveal the activation of YAP/TAZ signaling in both CAAs and BECN1-deficient adipocytes, inducing adipocyte dedifferentiation and formation of a malignant TME. The additional deletion of YAP/TAZ from BaKO mice significantly restores the lipodystrophy and inflammatory phenotypes, leading to tumor regression. Furthermore, mice fed a high-fat diet (HFD) exhibit decreased BECN1 and increased YAP/TAZ expression in their adipose tissues. Treatment with the YAP/TAZ inhibitor, verteporfin, suppresses tumor progression in BaKO and HFD-fed mice, highlighting its efficacy against mice with metabolic dysregulation. Overall, our findings provide insights into the key mediators of CAA and their significance in developing a TME, thereby suggesting a viable approach targeting adipocyte homeostasis to suppress cancer growth.

Abstract 15735: Antibody-Based Plasma Proteomics Profiling Reveals New Markers of Cardiorespiratory Fitness

Background: Plasma proteins can be biomarkers of cardiovascular health status but also physiologic effectors that mediate health benefits. Cardiorespiratory fitness (CRF) is an integrative measure of cardiovascular and metabolic health and independent predictor of future cardiovascular disease (CVD) and mortality risk, however limited knowledge exists regarding its molecular transducers. We sought to expand upon prior proteomic studies of CRF using an antibody-based technology (Olink TM ). Hypothesis: Olink proteomic profiling will identify new markers and potential mediators of CRF. Methods: We measured plasma proteins (N=1,472) using Olink’s platform in a pilot study within the HERITAGE Family Study (N=209 participants, mean age=34 years, 56% female, 36% Black) before and after 20 weeks of endurance exercise training (ET). We performed multivariable linear regression to measure the association between protein levels and CRF measured by CPET (VO 2 max in ml*kg -1 *min -1 ) adjusting for age and sex. Lean body mass was measured by hydrostatic weighing. Protein changes after ET were assessed using paired Student’s t-tests. Results: We identified 70 proteins significantly associated (FDR q <0.05) with VO 2 max. Among these, 14 have not previously been measured in the context of CRF, including perilipin-1, a modulator of lipid homeostasis in adipocytes (beta=-3.8, q=2.4x10 -4 ); latent-transforming growth factor beta-binding protein 3 (beta=-2.6, q=1.3x10 -3 ), a key regulator of TGF-beta activation; and hydroxysteroid 11-beta dehydrogenase 1 (beta=3.2, q=1.2x10 -3 ), which regulates cortisol metabolism. Carbonic anhydrase (CA) XIV (CA14; beta=5.4, q=1.3x10 -8 ), a member of the CA family with extracellular activity, had the strongest positive association with VO 2 max in our primary model as well as after further adjusting VO 2 max for lean body mass. Further, CA14 levels increased significantly after ET (log2 fold change: 0.14, q=0.007). Conclusions: Antibody-based plasma proteomics profiling identified new markers of CRF, including a CA isoform that increases after ET. These findings motivate further study of CA14’s mechanistic role in CA14 and expanded proteomics profiling to investigate molecular transducers of CRF.

Notch Signaling Regulates Mouse Perivascular Adipose Tissue Function via Mitochondrial Pathways.

Perivascular adipose tissue (PVAT) regulates vascular function by secreting vasoactive substances. In mice, Notch signaling is activated in the PVAT during diet-induced obesity, and leads to the loss of the thermogenic phenotype and adipocyte whitening due to increased lipid accumulation. We used the Adiponectin-Cre (Adipoq-Cre) strain to activate a ligand-independent Notch1 intracellular domain transgene (N1ICD) to drive constitutive Notch signaling in the adipose tissues (N1ICD;Adipoq-Cre). We previously found that constitutive activation of Notch1 signaling in the PVAT phenocopied the effects of diet-induced obesity. To understand the downstream pathways activated by Notch signaling, we performed a proteomic analysis of the PVAT from control versus N1ICD;Adipoq-Cre mice. This comparison identified prominent changes in the protein signatures related to metabolism, adipocyte homeostasis, mitochondrial function, and ferroptosis. PVAT-derived stromal vascular fraction cells were derived from our mouse strains to study the cellular and molecular phenotypes during adipogenic induction. We found that cells with activated Notch signaling displayed decreased mitochondrial respiration despite similar levels of adipogenesis and mitochondrial number. We observed variable regulation of the proteins related to mitochondrial dynamics and ferroptosis, including PHB3, PINK1, pDRP1, and the phospholipid hydroperoxidase GPX4. Mitochondria regulate some forms of ferroptosis, which is a regulated process of cell death driven by lipid peroxidation. Accordingly, we found that Notch activation promoted lipid peroxidation and ferroptosis in PVAT-derived adipocytes. Because the PVAT phenotype is a regulator of vascular reactivity, we tested the effect of Notch activation in PVAT on vasoreactivity using wire myography. The aortae from the N1ICD;Adipoq-Cre mice had increased vasocontraction and decreased vasorelaxation in a PVAT-dependent and age-dependent manner. Our data provide support for the novel concept that increased Notch signaling in the adipose tissue leads to PVAT whitening, impaired mitochondrial function, increased ferroptosis, and loss of a protective vasodilatory signal. Our study advances our understanding of how Notch signaling in adipocytes affects mitochondrial dynamics, which impacts vascular physiology.

The regulatory role of adipocyte mitochondrial homeostasis in metabolism-related diseases.

Adipose tissue is the most important energy storage organ in the body, maintaining its normal energy metabolism function and playing a vital role in keeping the energy balance of the body to avoid the harm caused by obesity and a series of related diseases resulting from abnormal energy metabolism. The dysfunction of adipose tissue is closely related to the occurrence of diseases related to obesity metabolism. Among various organelles, mitochondria are the main site of energy metabolism, and mitochondria maintain their quality through autophagy, biogenesis, transfer, and dynamics, which play an important role in maintaining metabolic homeostasis of adipocytes. On the other hand, mitochondria have mitochondrial genomes which are vulnerable to damage due to the lack of protective structures and their proximity to sites of reactive oxygen species generation, thus affecting mitochondrial function. Notably, mitochondria are closely related to other organelles in adipocytes, such as lipid droplets and the endoplasmic reticulum, which enhances the function of mitochondria and other organelles and regulates energy metabolism processes, thus reducing the occurrence of obesity-related diseases. This article introduces the structure and quality control of mitochondria in adipocytes and their interactions with other organelles in adipocytes, aiming to provide a new perspective on the regulation of mitochondrial homeostasis in adipocytes on the occurrence of obesity-related diseases, and to provide theoretical reference for further revealing the molecular mechanism of mitochondrial homeostasis in adipocytes on the occurrence of obesity-related diseases.

ATF4 knockdown in macrophage impairs glycolysis and mediates immune tolerance by targeting HK2 and HIF-1α ubiquitination in sepsis

Strengthened glycolysis is crucial for the macrophage pro-inflammatory response during sepsis. Activating transcription factor 4 (ATF4) plays an important role in regulating glucose and lipid metabolic homeostasis in hepatocytes and adipocytes. However, its immunometabolic role in macrophage during sepsis remains largely unknown. In the present study, we found that the expression of ATF4 in peripheral blood mononuclear cells (PBMCs) was increased and associated with glucose metabolism in septic patients. Atf4 knockdown specifically decreased LPS-induced spleen macrophages and serum pro-inflammatory cytokines levels in mice. Moreover, Atf4 knockdown partially blocked LPS-induced pro-inflammatory cytokines, lactate accumulation and glycolytic capacity in RAW264.7. Mechanically, ATF4 binds to the promoter region of hexokinase II (HK2), and interacts with hypoxia inducible factor-1α (HIF-1α) and stabilizes HIF-1α through ubiquitination modification in response to LPS. Furthermore, ATF4-HIF-1α-HK2-glycolysis axis launches pro-inflammatory response in macrophage depending on the activation of mammalian target of rapamycin (mTOR). Importantly, Atf4 overexpression improves the decreased level of pro-inflammatory cytokines and lactate secretion and HK2 expression in LPS-induced tolerant macrophages. In conclusion, we propose a novel function of ATF4 as a crucial glycolytic activator contributing to pro-inflammatory response and improving immune tolerant in macrophage involved in sepsis. So, ATF4 could be a potential new target for immunotherapy of sepsis.

Targeting adipocyte ESRRA rebalances bone and marrow adipocyte homeostasis through opposite regulation of LEPTIN and SPP1

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Mechanotransduction regulates inflammation responses of epicardial adipocytes in cardiovascular diseases.

Adipose tissue is a crucial regulator in maintaining cardiovascular homeostasis by secreting various bioactive products to mediate the physiological function of the cardiovascular system. Accumulating evidence shows that adipose tissue disorders contribute to several kinds of cardiovascular disease (CVD). Furthermore, the adipose tissue would present various biological effects depending on its tissue localization and metabolic statuses, deciding the individual cardiometabolic risk. Crosstalk between adipose and myocardial tissue is involved in the pathophysiological process of arrhythmogenic right ventricular cardiomyopathy (ARVC), cardiac fibrosis, heart failure, and myocardial infarction/atherosclerosis. The abnormal distribution of adipose tissue in the heart might yield direct and/or indirect effects on cardiac function. Moreover, mechanical transduction is critical for adipocytes in differentiation, proliferation, functional maturity, and homeostasis maintenance. Therefore, understanding the features of mechanotransduction pathways in the cellular ontogeny of adipose tissue is vital for underlining the development of adipocytes involved in cardiovascular disorders, which would preliminarily contribute positive implications on a novel therapeutic invention for cardiovascular diseases. In this review, we aim to clarify the role of mechanical stress in cardiac adipocyte homeostasis and its interplay with maintaining cardiac function.

Placental mesenchymal stem cells restore glucose and energy homeostasis in obesogenic adipocytes.

Obesity (Ob) depicts a state of energy imbalance(s) being characterized by the accumulation of excessive fat and which predisposes to several metabolic diseases. Mesenchymal stem cells (MSCs) represent a promising option for addressing obesity and its associated metabolic co-morbidities. The present study aims at assessing the beneficial effects of human placental MSCs (P-MSCs) in mitigating Ob-associated insulin resistance (IR) and mitochondrial dysfunction both in vivo and in vitro. Under obesogenic milieu, adipocytes showed a significant reduction in glucose uptake, and impaired insulin signaling with decreased expression of UCP1 and PGC1α, suggestive of dysregulated non-shivering thermogenesis vis-a-vis mitochondrial biogenesis respectively. Furthermore, obesogenic adipocytes demonstrated impaired mitochondrial respiration and energy homeostasis evidenced by reduced oxygen consumption rate (OCR) and blunted ATP/NAD+/NADP+ production respectively. Interestingly, co-culturing adipocytes with P-MSCs activated PI3K-Akt signaling, improved glucose uptake, diminished ROS production, enhanced mitochondrial OCR, improved ATP/NAD+/NADP+ production, and promoted beiging of adipocytes evidenced by upregulated expression of PRDM16, UCP1, and PGC1α expression. In vivo, P-MSCs administration increased the peripheral blood glucose uptake and clearance, and improved insulin sensitivity and lipid profile with a coordinated increase in the ratio of ATP/ADP and NAD+ and NADP+ in the white adipose tissue (WAT), exemplified in WNIN/GR-Ob obese mutant rats. In line with in vitro findings, there was a significant reduction in adipocyte hypertrophy, increased mitochondrial staining, and thermogenesis. Our findings advocate for a therapeutic application of P-MSCs for improving glucose and energy homeostasis, i.e., probably restoring non-shivering thermogenesis towards obesity management.

Modulation of adipose inflammation by cellular retinoic acid-binding protein 1

ObjectivesObesity, a metabolic syndrome, is known to be related to inflammation, especially adipose tissue inflammation. Cellular interactions within the expanded white adipose tissue (WAT) in obesity contribute to inflammation and studies have suggested that inflammation is triggered by inflamed adipocytes that recruit M1 macrophages into WAT. What causes accumulation of unhealthy adipocytes is an important topic of investigation. This study aims to understand the action of Cellular Retinoic Acid Binding Protein 1 (CRABP1) in WAT inflammation.MethodsEight weeks-old wild type (WT) and Crabp1 knockout (CKO) mice were fed with a normal diet (ND) or high-fat diet (HFD) for 8 weeks. Body weight and food intake were monitored. WATs and serum were collected for cellular and molecular analyses to determine affected signaling pathways. In cell culture studies, primary adipocyte differentiation and bone marrow-derived macrophages (BMDM) were used to examine adipocytes’ effects, mediated by CRABP1, in macrophage polarization. The 3T3L1-adipocyte was used to validate relevant signaling pathways.ResultsCKO mice developed an obese phenotype, more severely under high-fat diet (HFD) feeding. Further, CKO’s WAT exhibited a more severe inflammatory state as compared to wild type (WT) WAT, with a significantly expanded M1-like macrophage population. However, this was not caused by intrinsic defects of CKO macrophages. Rather, CKO adipocytes produced a significantly reduced level of adiponectin and had significantly lowered mitochondrial DNA content. CKO adipocyte-conditioned medium, compared to WT control, inhibited M2-like (CD206+) macrophage polarization. Mechanistically, defects in CKO adipocytes involved the ERK1/2 signaling pathway that could be modulated by CRABP1.ConclusionsThis study shows that CRABP1 plays a protective role against HFD-induced WAT inflammation through, in part, its regulation of adiponectin production and mitochondrial homeostasis in adipocytes, thereby modulating macrophage polarization in WAT to control its inflammatory potential.

Adipocyte-derived kynurenine promotes obesity and insulin resistance by activating the AhR/STAT3/IL-6 signaling

Aberrant amino acid metabolism is a common event in obesity. Particularly, subjects with obesity are characterized by the excessive plasma kynurenine (Kyn). However, the primary source of Kyn and its impact on metabolic syndrome are yet to be fully addressed. Herein, we show that the overexpressed indoleamine 2,3-dioxygenase 1 (IDO1) in adipocytes predominantly contributes to the excessive Kyn, indicating a central role of adipocytes in Kyn metabolism. Depletion of Ido1 in adipocytes abrogates Kyn accumulation, protecting mice against obesity. Mechanistically, Kyn impairs lipid homeostasis in adipocytes via activating the aryl hydrocarbon receptor (AhR)/Signal transducer and activator of transcription 3 /interleukin-6 signaling. Genetic ablation of AhR in adipocytes abolishes the effect of Kyn. Moreover, supplementation of vitamin B6 ameliorated Kyn accumulation, protecting mice from obesity. Collectively, our data support that adipocytes are the primary source of increased circulating Kyn, while elimination of accumulated Kyn could be a viable strategy against obesity.

Di-(2-ethylhexyl) phthalate substitutes accelerate human adipogenesis through PPARγ activation and cause oxidative stress and impaired metabolic homeostasis in mature adipocytes.

The obesity pandemic is presumed to be accelerated by endocrine disruptors such as phthalate-plasticizers, which interfere with adipose tissue function. With the restriction of the plasticizer di-(2-ethylhexyl)-phthalate (DEHP), the search for safe substitutes gained importance. Focusing on the master regulator of adipogenesis and adipose tissue functionality, the peroxisome proliferator-activated receptor gamma (PPARγ), we evaluated 20 alternative plasticizers as well as their metabolites for binding to and activation of PPARγ and assessed effects on adipocyte lipid accumulation. Among several compounds that showed interaction with PPARγ, the metabolites MINCH, MHINP, and OH-MPHP of the plasticizers DINCH, DINP, and DPHP exerted the highest adipogenic potential in human adipocytes. These metabolites and their parent plasticizers were further analyzed in human preadipocytes and mature adipocytes using cellular assays and global proteomics. In preadipocytes, the plasticizer metabolites significantly increased lipid accumulation, enhanced leptin and adipsin secretion, and upregulated adipogenesis-associated markers and pathways, in a similar pattern to the PPARγ agonist rosiglitazone. Proteomics of mature adipocytes revealed that both, the plasticizers and their metabolites, induced oxidative stress, disturbed lipid storage, impaired metabolic homeostasis, and led to proinflammatory and insulin resistance promoting adipokine secretion. In conclusion, the plasticizer metabolites enhanced preadipocyte differentiation, at least partly mediated by PPARγ activation and, together with their parent plasticizers, affected the functionality of mature adipocytes similar to reported effects of a high-fat diet. This highlights the need to further investigate the currently used plasticizer alternatives for potential associations with obesity and the metabolic syndrome.

Early Life Stress Increases Lipid Storage in Female Mice Fed a High Fat Diet via MR Activation in Adipocytes

We have previously shown that Maternal Separation and Early Weaning (MSEW), a mouse model of early life stress, exacerbates high fat diet (HF)‐induced obesity only in female offspring. Obese female MSEW mice display increased circulating and adrenal‐derived aldosterone and increased gWAT‐derived corticosterone compared with controls (C). Mineralocorticoid receptor (MR) activation has been shown to be critical in the regulation of the differentiation process of pre‐adipocytes into mature adipocytes and overall adipocyte homeostasis. The aim of this study was to determine the role of MR in the mechanism by which MSEW induces perigonadal hypertrophy in female mice fed a high fat diet (HF). MSEW and C mice were weaned onto a HF (60 % Kcal from fat). After 20 weeks, gonadal white adipose tissue (gWAT) was collected to conduct: 1) lipidomic analysis and markers of whitening, 2) collagenase digestion followed by magnetic activated cell sorting for isolation of preadipocytes for RNAseq, and 3) in vitro lipolysis assay. Another subset of mice was randomized to receive vehicle (50% Ora swift in water) or a MR blocker, spironolactone (Spiro, 100 mg/kg/day), for 2 weeks. Female MSEW mice showed increased adiposity along with reduced mitochondrial DNA density (0.81±0.09 and 1.08±0.07 mtDNA/gDNA, p<0.05 MSEW vs. C, respectively). Also, female MSEW mice displayed an increase of over 20 triacyclglycerols TAG, including a 6‐fold increase in 44:2/FA 18:2+NH4 (p<0.05 vs. C). Isolated mature adipocyte RNAseq revealed a 10‐fold downregulation of Aquaglycerolporin 3 (AQP3) in MSEW mice, a channel in adipocytes responsible for glycerol efflux (p<0.05 vs. C). Western blot analysis confirmed this reduction (0.40±0.08 and 1.0±0.14 AQP3/HSP90 p<0.05 MSEW vs. C, respectively). Spiro treatment induced a significant fat mass loss in obese MSEW females (‐3.5±0.9 and ‐1.0±0.5 delta fat mass (%BW) p<0.05 MSEW vs. C, respectively). Increased intracellular glycerol in vehicle‐treated MSEW mice was reduced to levels comparable to controls after Spiro treatment (1.08±0.2 and 1.64±0.12 mg glycerol/mg tissue, p<0.05 MSEW vs. C, respectively) while Spiro also decreased basal and stimulated released glycerol in MSEW mice (p<0.05). There were no differences in plasma glycerol between groups. It has been shown that aldosterone modulates AQP3 expression via MR signaling; however, Spiro treatment did not modify AQP3 protein expression. Overall, this data suggests that MR may play a role in adipose tissue hypertrophy as displayed by MSEW mice by preventing glycerol release in favor of triglyceride formation and storage, suggesting a role for impaired lipolysis that is independent of reduced AQP3 protein expression in adipocyte hypertrophy displayed by obese female MSEW mice.

Cholecystokinin promotes functional expression of the aquaglycerol channel aquaporin 7 in adipocytes.

Cholecystokinin (CCK) promotes triglyceride storage and adiponectin production in white adipose tissue (WAT), suggesting that CCK modulates WAT homeostasis. Our goal was to investigate the role of CCK in regulating the expression and function of the aquaglycerol channel aquaporin 7 (AQP7), a protein that is pivotal for maintaining adipocyte homeostasis and preserving insulin responsiveness. The effect of the bioactive fragment of CCK, CCK-8, in regulating adipose AQP7 expression and glycerol efflux was assessed in rats as well as in preadipocytes. Moreover, the involvement of insulin receptors in the effects of CCK-8 was characterized in preadipocytes lacking insulin receptors. CCK-8 induced AQP7 gene expression in rat WAT, concomitantly increasing plasma glycerol concentration. In isolated preadipocytes, CCK-8 also enhanced both AQP7 expression and glycerol leakage. The effects of CCK-8 were independent of the lipolysis rate, as CCK-8 failed to promote fatty acid release by adipocytes. In addition, CCK-8 did not enhance hormone sensitive lipase phosphorylation, which is the rate-limiting step of lipolysis. Moreover, the effects of CCK-8 were dependent on the activation of protein kinase B and PPARγ. Silencing insulin receptor expression inhibited CCK-8-induced Aqp7 expression in preadipocytes. Furthermore, insulin enhanced the effect of CCK-8. CCK regulates AQP7 expression and function, and this effect is dependent on insulin. Accordingly, CCK receptor agonists could be suitable for preserving and improving insulin responsiveness in WAT.

Not Enough Fat: Mouse Models of Inherited Lipodystrophy.

Lipodystrophies belong to the heterogenous group of syndromes in which the primary defect is a generalized or partial absence of adipose tissue, which may be congenital or acquired in origin. Lipodystrophy should be considered in patients manifesting the combination of insulin resistance (with or without overt diabetes), dyslipidemia and fatty liver. Lipodystrophies are classified according to the etiology of the disease (genetic or acquired) and to the anatomical distribution of adipose tissue (generalized or partial). The mechanism of adipose tissue loss is specific to each syndrome, depending on the biological function of the mutated gene. Mice models, together with cellular studies have permitted clarification of the mechanisms by which human mutations deeply compromise adipocyte homeostasis. In addition, rodent models have proven to be crucial in deciphering the cardiometabolic consequences of the lack of adipose tissue such as NAFLD, muscle insulin resistance and cardiomyopathy. More precisely, tissue-specific transgenic and knockout mice have brought new tools to distinguish phenotypic traits that are the consequences of lipodystrophy from those that are cell-autonomous. In this review, we discuss the mice models of lipodystrophy including those of inherited human syndromes of generalized and partial lipodystrophy. We present how these models have demonstrated the central role of white adipose tissue in energetic homeostasis in general, including insulin sensitivity and lipid handling in particular. We underscore the differences reported with the human phenotype and discuss the limit of rodent models in recapitulating adipose tissue primary default. Finally, we present how these mice models have highlighted the function of the causative-genes and brought new insights into the pathophysiology of the cardiometabolic complications associated with lipodystrophy.

Seipin Deficiency as a Model of Severe Adipocyte Dysfunction: Lessons from Rodent Models and Teaching for Human Disease

Obesity prevalence is increasing worldwide, leading to cardiometabolic morbidities. Adipocyte dysfunction, impairing white adipose tissue (WAT) expandability and metabolic flexibility, is central in the development of obesity-related metabolic complications. Rare syndromes of lipodystrophy characterized by an extreme paucity of functional adipose tissue should be considered as primary adipocyte dysfunction diseases. Berardinelli-Seip congenital lipodystrophy (BSCL) is the most severe form with a near absence of WAT associated with cardiometabolic complications such as insulin resistance, liver steatosis, dyslipidemia, and cardiomyopathy. Twenty years ago, mutations in the BSCL2 gene have been identified as the cause of BSCL in human. BSCL2 encodes seipin, an endoplasmic reticulum (ER) anchored protein whose function was unknown back then. Studies of seipin knockout mice or rats demonstrated how seipin deficiency leads to severe lipodystrophy and to cardiometabolic complications. At the cellular levels, seipin is organized in multimers that are particularly enriched at ER/lipid droplet and ER/mitochondria contact sites. Seipin deficiency impairs both adipocyte differentiation and mature adipocyte maintenance. Experiments using adipose tissue transplantation in seipin knockout mice and tissue-specific deletion of seipin have provided a large body of evidence that liver steatosis, cardiomyopathy, and renal injury, classical diabetic complications, are all consequences of lipodystrophy. Rare adipocyte dysfunctions such as in BSCL are the key paradigm to unravel the pathways that control adipocyte homeostasis. The knowledge gathered through the study of these pathologies may bring new strategies to maintain and improve adipose tissue expandability.

The role of dendritic cells in the immune niche of the peritoneum.

Dendritic cells (DCs) are professional antigen presenting cells that play an important role in the induction of T cell responses. Different subsets (cDC1s, cDC2s, pDCs, and moDCs) were described based on the expression of different surface markers and functions. In the context of peritoneum, DCs are also a key population cell orchestrating immune responses against pathogens, malignant cells and tissue-damage. Furthermore, they play an important role in the promotion of an anti-inflammatory microenvironment, which is necessary to maintain tolerance and adipocyte homeostasis. The aim of this review is to summarize the current knowledge of the functional and phenotypic features of peritoneal DCs and shed some light on the importance of these cells within this unique cavity and its associated components: the omentum, the mesentery and gut-associated lymphoid tissue (GALT).

Immune and non-immune functions of adipose tissue leukocytes.

Adipose tissue is a complex dynamic organ with whole-body immunometabolic influence. Much of the work into understanding the role of immune cells in adipose tissue has been in the context of obesity. These investigations have also uncovered a range of typical (immune) and non-typical functions exerted by adipose tissue leukocytes. Here we provide an overview of the adipose tissue immune system, including its role as an immune reservoir in the whole-body response to infection and as a site of parasitic and viral infections. We also describe the functional roles of specialized immunological structures found within adipose tissue. However, our main focus is on the recently discovered 'non-immune' functions of adipose tissue immune cells, which include the regulation of adipocyte homeostasis, as well as responses to changing nutrient status and body temperature. In doing so, we outline the therapeutic potential of the adipose tissue immune system in health and disease.

Dietary Iron Deficiency Modulates Adipocyte Iron Homeostasis, Adaptive Thermogenesis, and Obesity in C57BL/6 Mice

BackgroundAdaptive thermogenesis is an iron-demanding pathway, significantly contributing to whole-body energy expenditure. However, the effects of iron-deficient diets on adaptive thermogenesis and obesity remain unknown. ObjectivesWe aimed to determine the impact of dietary iron deficiency on iron homeostasis in adipocytes, adaptive thermogenic capacity, and metabolic consequences in obesity. MethodsC57BL/6 male mice were assigned to either the iron-adequate (IA, 35 ppm) or the iron-deficient group (ID, 3 ppm) at weaning. Upon 8 wk of age, both IA and ID groups received an isocaloric high-fat diet (45% kcal from fat) for 10 wk, maintaining the same iron content. Mice (n = 8) were used to determine the iron status at the systemic and tissue levels and lipid metabolism and inflammatory signaling in adipose tissue. The same mice were used to evaluate cold tolerance (4°C) for 3 h. For assessing adaptive thermogenesis, mice (n = 5) received an intraperitoneal injection of β3-adrenoceptor agonist CL316243 (CL) for 5 d. ResultsCompared with the IA group, the ID group had nonanemic iron deficiency, lower serum ferritin (42.8%, P < 0.01), and greater weight gain (8.67%, P < 0.05) and insulin resistance (159%, P < 0.01), partly due to reduced AMP-activated protein kinase activation (61.0%, P < 0.05). Upon cold exposure, the ID group maintained a core body temperature 2°C lower than the IA group. The ID group had lower iron content (47.0%, P < 0.01) in the inguinal adipose tissue (iWAT) than the IA group, which was associated with impaired adaptive thermogenesis. In response to CL, ID mice showed decreased heat production (P < 0.01) and defective upregulation of beige adipocyte-specific markers, including uncoupling protein 1 (41.1%, P < 0.001), transferrin receptor 1 (47.5%, P < 0.001), and mitochondrial respiratory chain complexes (P < 0.05) compared with IA mice. ConclusionsDietary iron deficiency deregulates iron balance in the iWAT and impairs adaptive thermogenesis, thereby escalating the diet-induced weight gain in C57BL/6 mice.

N4BP2L1 interacts with dynactin and contributes to GLUT4 trafficking and glucose uptake in adipocytes.

ABSTRACTAims/IntroductionIt was reported previously that N4bp2l1 expression increases in 3T3‐L1 cells in a differentiation‐dependent manner and N4bp2l1 knockdown suppresses adipocyte differentiation. However, the physiological function of N4BP2L1 in adipocytes remains unknown. This study aimed to elucidate the physiological mechanism of N4bp2l1 expression and the role of N4BP2L1 in the physiological function of adipocytes.Materials and MethodsAnalysis of gene expression levels of N4bp2l1 in adipose tissue during feeding in mice was conducted. Identification of transcription factors that regulate N4bp2l1 expression was conducted using a reporter assay. Investigation of N4BP2L1‐interacting proteins was carried out using immunoprecipitation. A GLUT4 translocation assay and a glucose uptake assay in 3T3‐L1 adipocytes were performed using N4bp2l1 overexpression and knockdown adenovirus.ResultsThe results indicated that N4bp2l1 is a novel FoxO1 target gene and its expression is controlled by the insulin‐mediated regulation of FoxO1. N4BP2L1 interacts with dynactin, which binds to the microtubule motor dynein, indicating that N4BP2L1 is involved in GLUT4 trafficking and glucose uptake in 3T3‐L1 adipocytes.ConclusionsOur results suggest that N4BP2L1 is involved in adipocyte homeostasis by interacting with dynein–dynactin and affecting GLUT4‐mediated glucose uptake and the insulin signaling pathway.

Adipocyte Induced Antagonism of ALL Growth Highlights a Novel Inhibitory Niche and Potential Therapeutic Opportunity

The importance of Bone Marrow Microenvironment (BMM) in driving ALL progression is widely recognised however the nature of the leukaemia niche remains unclear. To gain specific insight, we assessed the evolving composition of ALL- BMMs both in primary human disease and experimental models. Strikingly, BMMs in both human ALL (n=6) and Nalm-6 ALL xenografts (n =5) exhibited severely depleted adipocyte densities (98.2 and 75.7% reduction vs control, p <0.05) with adipocyte homeostasis resetting upon remission attainment. To assess the potential biological significance of the inverse correlation between ALL and adipocytes we co-cultured a panel of ALL cell lines (Nalm-6, REH and RS4;11) with both murine 3T3-L1 adipocytes as well as primary adipocytes differentiated from normal BM derived Mesenchymal stromal cells (MSC), assessing cellular outcomes. Surprisingly, both 3T3-L1 and BM-MSC derived adipocytes impaired growth of ALL cell lines in a time dependant fashion. In contrast, co-culture with primary osteoblasts and MSCs did not alter basal rates of cellular growth confirmingthat adipocytes inhibited ALL growth in a tissue specific manner.Mechanistically, adipocytes repressed the G1/G2/S/M cell cycle progression of ALL cells without enhancing apoptosis indicating that cell extrinsic signals derived from adipocytes induce cytostasis. Thus, impairment of adipocyte BMM's during ALL development may function to disable a stromally derived ALL suppressor. To further investigate the leukaemia inhibitory function of tissue adipocytes, we compared leukaemia development in adipocyte rich (tail BM, omental and gonadal fat) vs adipocyte poor environments (femoral/thoracic bones) using a xenotransplantation model (Figure 1). In vivo, Nalm-6 growth was significantly restrained in adipocyte rich tissue compared to adipocyte poor regions and adipocyte poor extramedullary control tissue. Similarly, patient derived xenografts (n =3) demonstrated delayed development in adipocyte rich regions recapitulating the cellular response of ALL cell lines. Consistent with the in vitro data, adipocyte imprinted ALL cells in vivo resided in a less active cell cycle state supporting the contention that adipocytes are a transducer of negative growth signals. To investigate the tumour suppressor mechanism controlling growth we performed transwell experiments revealing that, basal rates of cellular proliferation and cell cycling, could be restored following transwell separation consistent with contact/close proximity factor mediating adipocyte induced tumour suppressive signalling. In line with these results, RNA-Seq demonstrated upregulation in extracellular matrix receptor pathways (FDR q-val 0.14) together with downregulation of cell cycle genes (p <0.05) in adipocyte exposed ALL cell lines. Adipocytes correspondingly were reprogrammed by ALL environments as assessed by quantitative proteomics indicating a cooperative interplay between these cells. To further delineate the mechanism by which adipocytes are depleted in ALL-BMMs we investigated the MSC axis hypothesising that adipocyte development was disrupted. Significantly fewer MSCs expanded in ALL BM vs age matched control with a corresponding reduction in CFU's indicating that ALL deregulates the intrinsic self-renewal capacity of MSCs. We further compared the multidifferentiation potential of ALL-MSC vs control MSCs following developmental induction. Surprisingly we found that ALL-MSCs had enhanced capacity for adipogenic differentiation (3.93 ± 0.69 fold increase; n = 5; p= 0.01) without reciprocal disturbance in osteogenesis. Increased adipocyte commitment could be reproduced by exposing normal MSCs to leukaemic serum but not HSC cultures suggesting that the altered priming of ALL- MSCs towards adipocyte differentiation is induced via a leukaemia soluble factor. Collectively, our data suggests adipocyte depletion in leukaemia BMMs may be contributed to by repressed MSC growth and that whilst adipocyte primed MSC's accumulate, differentiation might be stalled through a blast specific mechanism.ConclusionOur results suggest that adipocyte microenvironments create an inhibitory niche for ALL cells consistent with a tumour suppressive function, dissecting how these inhibitory niches are disabled to promote ALL development could uncover a novel therapeutic avenue. [Display omitted] DisclosuresGribben:Karyopharm: Honoraria; Genentech/Roche: Honoraria; Abbvie: Honoraria; Acerta: Honoraria; Janssen: Honoraria; Kite: Honoraria; Pharmacyclics: Honoraria; TG Therapeutics: Honoraria; Celgene: Honoraria.